A new variant of
Methanothermobacter wolfeii
was isolated from an anaerobic digester using enrichment cultivation in anaerobic conditions. The new isolate was taxonomically identified via 16S rRNA gene sequencing and tagged as
M. wolfeii
BSEL. The whole genome of the new variant was sequenced and
de novo
assembled. Genomic variations between the BSEL strain and the type strain were discovered, suggesting evolutionary adaptations of the BSEL strain that conferred advantages while growing under a low concentration of nutrients.
M. wolfeii
BSEL displayed the highest specific growth rate ever reported for the
wolfeii
species (0.27 ± 0.03 h
−1
) using carbon dioxide (CO
2
) as unique carbon source and hydrogen (H
2
) as electron donor.
M. wolfeii
BSEL grew at this rate in an environment with ammonium (NH
4
+
) as sole nitrogen source. The minerals content required to cultivate the BSEL strain was relatively low and resembled the ionic background of tap water without mineral supplements. Optimum growth rate for the new isolate was observed at 64°C and pH 8.3. In this work, it was shown that wastewater from a wastewater treatment facility can be used as a low-cost alternative medium to cultivate
M. wolfeii
BSEL. Continuous gas fermentation fed with a synthetic biogas mimic along with H
2
in a bubble column bioreactor using
M. wolfeii
BSEL as biocatalyst resulted in a CO
2
conversion efficiency of 97% and a final methane (CH
4
) titer of 98.5%
v
, demonstrating the ability of the new strain for upgrading biogas to renewable natural gas.
IMPORTANCE
As a methanogenic archaeon,
Methanothermobacter wolfeii
uses CO
2
as electron acceptor, producing CH
4
as final product. The metabolism of
M. wolfeii
can be harnessed to capture CO
2
from industrial emissions, besides producing a drop-in renewable biofuel to substitute fossil natural gas. If used as biocatalyst in new-generation CO
2
sequestration processes,
M. wolfeii
has the potential to accelerate the decarbonization of the energy generation sector, which is the biggest contributor of CO
2
emissions worldwide. Nonetheless, the development of CO
2
sequestration archaeal-based biotechnology is still limited by an uncertainty in the requirements to cultivate methanogenic archaea and the unknown longevity of archaeal cultures. In this study, we report the adaptation, isolation, and phenotypic characterization of a novel variant of
M. wolfeii
, which is capable of maximum growth with minimal nutrients input. Our findings demonstrate the potential of this variant for the production of renewable natural gas, paving the way for the development of more efficient and sustainable CO
2
sequestration processes.